Bash retry function

retry.sh

# Retry a command with a fixed numer of times until it exits successfully,
# with exponential back off + 1.
# usage:
# $ source ./retry.sh
# $ retry echo "hello world"
# hello world
# $ retry false
# Retry 1/7: command exited with code 1, retrying in 2 seconds. Retrying...
# Retry 2/7: command exited with code 1, retrying in 3 seconds. Retrying...
# Retry 3/7: command exited with code 1, retrying in 5 seconds. Retrying...
# Retry 4/7: command exited with code 1, retrying in 9 seconds. Retrying...
# Retry 5/7: command exited with code 1, retrying in 17 seconds. Retrying...
# Retry 6/7: command exited with code 1, retrying in 33 seconds. Retrying...
# Retry 7/7: command exited with code 1, retrying in 65 seconds. Retrying...
# command exited with code 1, no more retries left.
#
function retry {
  local retries=7

  local count=0
  until "$@"; do
    exit=$?
    wait=$((2 ** $count + 1))
    count=$(($count + 1))
    if [ $count -lt $(($retries + 1)) ]; then
      echo -n "Retry $count/$retries: command exited with code $exit, retrying in $wait seconds. "
      sleep $wait
      echo "Retrying..."
    else
      echo "command exited with code $exit, no more retries left."
      return $exit
    fi
  done
  return 0
}